diff --git a/sphinx/domains/cpp.py b/sphinx/domains/cpp.py
index a932227a6..2ce107484 100644
--- a/sphinx/domains/cpp.py
+++ b/sphinx/domains/cpp.py
@@ -26,7 +26,9 @@ from sphinx.util.pycompat import UnicodeMixin
 from sphinx.util.docfields import Field, GroupedField
 
 """
-    Important note on ids:
+    Important note on ids
+    ----------------------------------------------------------------------------
+
     Multiple id generation schemes are used due to backwards compatibility.
     - v1: 1.2.3 <= version < 1.3
           The style used before the rewrite.
@@ -38,6 +40,19 @@ from sphinx.util.docfields import Field, GroupedField
     All versions are generated and attached to elements. The newest is used for
     the index. All of the versions should work as permalinks.
 
+
+    Tagnames
+    ----------------------------------------------------------------------------
+
+    Each desc_signature node will have the attribute 'sphinx_cpp_tagname' set to
+    - 'templateParams', if the line is on the form 'template<...>',
+    - 'declarator', if the line contains the name of the declared object.
+    No other desc_signature nodes should exist (so far).
+
+
+    Grammar
+    ----------------------------------------------------------------------------
+
     See http://www.nongnu.org/hcb/ for the grammar,
     or https://github.com/cplusplus/draft/blob/master/source/grammar.tex
     for the newest grammar.
@@ -755,6 +770,7 @@ class ASTTemplateDeclarationPrefix(ASTBase):
         _verify_description_mode(mode)
         for t in self.templates:
             templateNode = addnodes.desc_signature()
+            templateNode.sphinx_cpp_tagname = 'templateParams'
             t.describe_signature(templateNode, 'lastIsName', env, symbol)
             signode += templateNode
 
@@ -2172,6 +2188,7 @@ class ASTDeclaration(ASTBase):
         # let's pop it so we can add templates before that
         parentNode = signode.parent
         mainDeclNode = signode
+        mainDeclNode.sphinx_cpp_tagname = 'declarator'
         parentNode.pop()
 
         assert self.symbol